title: Bonding, antibonding and tunable optical forces in asymmetric membranes.
abstract: We demonstrate that tunable attractive (bonding) and repulsive (anti-bonding) forces can arise in highly asymmetric structures coupled to external radiation, a consequence of the bonding/anti-bonding level repulsion of guided-wave resonances that was first predicted in symmetric systems. Our focus is a geometry consisting of a photonic-crystal (holey) membrane suspended above an unpatterned layered substrate, supporting planar waveguide modes that can couple via the periodic modulation of the holey membrane. Asymmetric geometries have a clear advantage in ease of fabrication and experimental characterization compared to symmetric double-membrane structures. We show that the asymmetry can also lead to unusual behavior in the force magnitudes of a bonding/antibonding pair as the membrane separation changes, including nonmonotonic dependences on the separation. We propose a computational method that obtains the entire force spectrum via a single time-domain simulation, by Fourier-transforming the response to a short pulse and thereby obtaining the frequency-dependent stress tensor. We point out that by operating with two, instead of a single frequency, these evanescent forces can be exploited to tune the spring constant of the membrane without changing its equilibrium separation.
authors.affiliation: Department of Mathematics, Massachusetts Institute of Technology, Cambridge,Massachusetts 02139, USA. alexrod7@mit.edu
authors.forename: Alejandro W
authors.initials: AW
authors.lastname: Rodriguez
authors.forename: Alexander P
authors.initials: AP
authors.lastname: McCauley
authors.forename: Pui-Chuen
authors.initials: PC
authors.lastname: Hui
authors.forename: David
authors.initials: D
authors.lastname: Woolf
authors.forename: Eiji
authors.initials: E
authors.lastname: Iwase
authors.forename: Federico
authors.initials: F
authors.lastname: Capasso
authors.forename: Marko
authors.initials: M
authors.lastname: Loncar
authors.forename: Steven G
authors.initials: SG
authors.lastname: Johnson
mesh_terms: D003198:Computer Simulation; D008027:Light; D008567:Membranes, Artificial; D008962:Models, Theoretical; D052898:Optical Tweezers; D013314:Stress, Mechanical
chemical_list: D008567:Membranes, Artificial